JPS6387876A - Digital video signal synthesis circuit - Google Patents

Abstract

PURPOSE:To synthesize plural digital video signals easily by converting an RGB signal such as a character into a luminance/color difference signal, subtracting a switching signal component for pattern synthesis from a video signal and adding the signal of RGB system. CONSTITUTION:RGB signals C-E such as character signals are converted respectively into luminance/color difference signals Y2, U2, V2 by a YUV matrix circuit 20, digitized by A/D converters 3-5, and a switching signal (YS)B for pattern synthesis is digitized by the A/D converter 2 to obtain a signal Y' by subtracting the switching signal YS1. Further, a luminance signal Y3 of the character system is added to the signal Y' by an adder 24 to obtain a luminance signal Y'' being the synthesis of the video and character signal. Similarly, the color difference signal is processed. Thus, the video signal and the character signal are synthesized by a simple adder/subtractor circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital video signal synthesis circuit for synthesizing two digitized video and character signals.

BACKGROUND OF THE INVENTION In recent years, digital processing of video signals has been progressing, and application to digital television receivers is particularly popular, and is useful for improving image quality and functions.

Among these, video processing compatible with new media has become mainstream, such as displaying images by combining original video signals with RGB signals from teletext broadcasting, personal computers, etc. In addition, by applying digital signal processing technology to memory, there are many ways to improve image quality by increasing the scanning line density to twice that of conventional image signals, which is called double-speed conversion, and creating more detailed images. It is being used.

An example of the conventional digital video signal synthesis apparatus mentioned above will be described below with reference to the drawings.

FIG. 4 shows a block diagram of a conventional digital video signal synthesis circuit. In FIG. 4, 1 is an A/D converter that digitizes a composite analog video signal;
2 is an A/D converter that digitizes the switching signal (called YS) B that synthesizes the video signal A and analog RCiB signals C, D, and E such as teletext broadcasting; 3 to 6 are RGB
An A/D converter 6 digitizes the signals C1D and E, and 6 converts the digitized video signal into a baseband luminance signal Y1.
and color difference signal U1. A digital signal demodulation circuit 7.8 demodulates the video signal Y1.V1. U1. Double speed conversion circuits convert V1 and RGE signals (R1, G1.B1) and switching signal Y81 to double the scanning line, and 9 to 16 convert the double speed converted digital signals into analog signals. D/A converter, 16 is a D/A converted video signal Y
5゜U5. V5J: RGBf conversion circuit that generates RGB signals; 17, RGB signals R4, G4 . B4 and character signals R3, G3. 18 is an image display device; a signal synthesis circuit that synthesizes B3 using a switching signal YS3;

The digital video signal synthesis circuit having the double speed conversion circuit configured as described above will be described below with reference to the signal waveforms shown in FIG.

In FIG. 4, a video signal A is a composite video signal as shown in FIG. . There are various demodulation methods, but in general, the luminance signals Y1 and (c) shown in FIG.
It is demodulated into a red color difference signal v1 and a blue color difference signal U1 shown in (d). Here, Fig. 5(b), (C),
(d) The following digital signals are shown as analog waveforms for the sake of explanation.

The demodulated Yl, Ul, and V1 signals are applied to a double speed conversion circuit F, where they are subjected to double speed conversion. Here, the configuration of the double speed conversion circuit is shown in FIG. -Generally, double-speed conversion uses line memory (horizontal scanning - stores data from a book) or field/frame memory (stores data for one screen or one picture). However, in FIG. 7, a configuration using a line memory will be described below.

In FIG. 7(δ), a line memory 19 stores data for one horizontal scanning period of the video signal.

The input data D1 is 1 as shown in FIG.
The line memory 1 is scanned using the write clock C1 (cycle T) shown in FIG.
9 as data H1. The written data is read out from the line memory by the read clock C2 shown in FIG. 7(f) using the read reference pulse P2 shown in FIG. Read out. Here, since the read clock C2 has a period T/2, which is half the period of the write clock C1, the read data D2 has a period τ of one horizontal scan, as shown in FIG. 7(q). Data HO' will be read twice. In this way, by using the line memory, it is possible to
)K, between the horizontal scanning signals indicated by solid lines,
By interpolating the signal shown in dashed lines, the scanning signal can be doubled in density.

As described above, the signal Y1.
U1. V1 is double-speed converted as shown in FIGS. 6(e), (f), and (cr), resulting in Ys and Us, respectively.

Get v5. Furthermore, the luminance signal Y6 and the color difference signals US and V6, which have been double-speed converted by the RGB conversion circuit 16, are converted to R as shown in FIGS. 6(h), (i), and (j).
GB signals R4, G4. Converted to B4. Generally RGB
The conversion circuit 16 satisfies the following combination formula.

Y5=0.3R4+0.59G440.11B4U 6
= -0,314-0,59G4 10.89B4V
5=0.7R4-0, 59G4-0.11B4 On the other hand, RGB input signals such as character signals are input to the A/D converter 3.4.5 as shown in FIG. 4C, D, and E. The signal is converted into a digital signal and added to the double speed conversion circuit (8). Also,
The switching signal (YS) B for synthesizing the screen is applied to the A/D converter 2, as shown in Fig. 4, and the double speed conversion circuit 8
added to. Signals YS, R, G, B (Fig. 6 OC),
(4), (e).

(n) respectively. Double speed converted signal YS2゜R
2, G2. B2 is a D/A converter 12, 13゜14.1
5, and the 6th m(0), ω>, (q), (r
) is the analog signal YS3. Ra, G3. Get B3.

The signals R4, G4. R4 and R3, G3. R3 is converted to YS by the image synthesis circuit 17.
The signal Rs is synthesized based on the signals.

G5. R6 is obtained and displayed on a display device 19 such as a CRT.

The synthesis circuit 17 is an analog switch, and is shown in FIG.
) in which the YS3 signal is at high level, the signals R3, G3 .
R3 is displayed, and during the low level section, signals R4, G4 . R
6 (8), (t),
A signal as shown in (u) can be obtained.

Problems to be Solved by the Invention However, with the above configuration, in a system having signal processing such as double speed conversion, the R
In order to synthesize the GB signals and display them on the screen, the RGB signals and the switching signal for screen synthesis are digitized, converted to double speed, and then D/A converted to display the screen in the double speed converted analog signal state. It is necessary to perform synthesis, and RG
A separate double-speed conversion circuit and D/A converter are required for the B signal input system.Furthermore, in double-speed analog screen synthesis, switching by the YS signal is generally as fast as 27MHz, and the switching circuit is required. There were problems such as signal delays due to high-speed switching and difficulty in accurately synthesizing signals.

In particular, in systems where video signal processing is digitized, if you try to perform screen compositing before double speed conversion, the video signal is simply converted to an analog signal, the screen is synthesized, and then the digital This has resulted in a complicated system that requires double speed conversion, and there has been a desire for a means to easily synthesize images in the digital signal domain.

In view of the above-mentioned problems, the present invention provides a digital and digital video signal synthesis circuit that can accurately synthesize digitized video signals and RGB signals such as character signals with a simple configuration. be.

Means for Solving the Problems In order to solve the above problems, the digital video signal synthesis circuit of the present invention uses a digital video signal (luminance/color difference) to
a subtracter that subtracts a digitized switching signal for synthesis; a circuit that converts an RGB signal such as a character signal into a luminance/color difference signal in the same format as a video signal from the subtracted signal; It consists of an adder that adds signals obtained by digitizing the RGB luminance/color difference signals.

Function: With this configuration, RGB signals such as characters are converted into luminance/color difference signals, making them in the same format as video signals, and first subtracting switching signal components for screen composition from the video signals. After that, screen synthesis is performed by adding RGB signals.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a digital video signal synthesis circuit in one embodiment of the present invention. In FIG. 1, 1 to 5 are A/D converters, 6 is a digital video signal demodulation circuit, 7 is a double speed conversion circuit, and 9 to 11 are D/A converters.
The converter, 16 is an RGB conversion circuit, and 18 is a CRT display device, which is the same as the configuration shown in FIG. 4. Also,
20 is a YUV matrix circuit, 21 to 23 are subtracters, 2
4 to 26 are adders.

The operation of the digital video signal synthesis circuit configured as described above will be explained below with reference to the signal waveforms shown in FIG. 2. In FIG. 1, first, a composite video signal A (see FIG. 2 (-)) is digitized by an A/D converter 1, and then converted into a digital video signal by a digital video signal demodulation circuit 6 as shown in FIG.
b), (C), and (d), the digital luminance/color difference signal Y1. U1. (2) Each signal is demodulated to 1.

Here, the waveforms in FIG. 2 are analog waveforms for the sake of explanation, and the numerical values represent amplitudes. On the other hand, Fig. 2(e), (f
), (RGB signals C, D, E such as character signals as shown in (J) are processed by the YUV matrix circuit 20,
As shown in FIG. 2(h), (i), and (i), the airiness/color difference signal Y2. U2. V2 and A
/D converters 3, 4.5 digitize.

At this time, the YUV matrix circuit 2o is created from RGB signals, and the relationship generally satisfies the following equation.

Y2=0.3R+0.59G+0.11BU2=B-Y
2 V2=R-Y2 Furthermore, the switching signal (YS)B for screen synthesis shown in FIG. 3(k) is digitized by the A/D converter 2,
It is added to the subtracter as the Y81 signal.

As shown in FIG. 3(k), the Y81 signal outputs a character signal when the signal level is high, and outputs a video signal when the signal level is low. The switching signal YS is originally a switching signal, but if it is processed as a 1-bit signal, jitter will occur in the cycle of the sampling clock, so it is processed as an n-bit signal. therefore,
The switching takes place in stages.

Next, a method of screen composition centered on the YS signal will be described.

In this case, the luminance signal will be explained as a representative. By subtracting the switching signal Y81 shown in FIG. 3(k) from the image luminance signal Y1 shown in FIG. 3(O) by the subtracter 21 in FIG. Obtain a signal Y' that makes
The component of the video luminance signal Y1 becomes smaller. Furthermore, since subtraction is performed, switching is performed smoothly in stages. Furthermore, the character luminance signal Y3 shown in FIG. 3) is added to the signal Y' by the adder 24, so that K yy< as shown in FIG.
A luminance signal Y" is obtained by combining the video and character signals. At this time, the hatched part in FIG. 3(o) becomes the part of the combined character signal.

Furthermore, the synthesized luminance signal Y" is double-speed converted by the double-speed conversion circuit 7, and the waveform Y4 shown in FIG. 3(p) is
get. After that, the signal Y4 is D/A converted.
is converted into an analog signal by Similarly, color difference signals are also processed to obtain signals Us and Vs. And R.G.
In the B conversion circuit 16, Ys.

In order to drive the Us, Vs multiplied signal CRT display device 18, the RGB signals R5, G5 . It is converted to BS and displayed.

As described above, according to this embodiment, RGB of character signals etc.
Convert input signal to luminance/color difference signal and digitize 1-1
Furthermore, by subtracting the switching signal YS for screen synthesis from the demodulated luminance and color difference signals of the video signal system, and then adding the luminance and color difference signals of the character signal system,
A video signal and a character signal can be synthesized with a simple addition/subtraction circuit without using a special multiplier or adding a double-speed conversion circuit and a D/A converter for the character signal system.

Effects of the Invention As described above, the present invention provides the following advantages:
By providing a subtracter that subtracts a switching signal for screen composition and an adder that adds a second digital video signal such as a character signal to the subtracted signal, multiple digital video signals can be combined. Can be easily synthesized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a digital video signal synthesis circuit according to an embodiment of the present invention, FIGS. 2 and 3 are operational waveform diagrams thereof, and FIG. 4 is a block diagram of a conventional digital video signal synthesis circuit. 5 and 6 are operational waveform diagrams thereof, and FIG. 7 is a block diagram and waveform diagram of a specific example of the double speed conversion circuits 7 and 8. 1 to 6... A/D converter, 6... Signal demodulation circuit, 7... Double speed modulation circuit, 9 to 11...
...D/A converter, 16...RGB conversion circuit, 18...CRT display circuit, 21-23...
...Subtraction circuit, 24-26...Addition circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure (720, 5----------- (j) -洟゛-→31- Figure 3, Figure 5, Figure 6

Claims (2)

[Claims] (1) A plurality of first bit digital signals, a plurality of second m-bit digital signals, a third n-bit digital signal, and the plurality of first digital signals. , a digital video signal synthesis circuit comprising a subtraction circuit that commonly subtracts a third digital signal, and an addition circuit that adds the subtracted signal and the plurality of second digital signals. . (2) Digital video signal synthesis according to claim 1, wherein the plurality of first m-bit digital signals and the plurality of second m-bit digital signals are a video luminance signal and a color difference signal. circuit.